1. Field of the Invention
The present invention relates to backlash-free speed reducing devices and, more particularly, to a backlash-free speed reducing device designed to allow all the rotatable cylinders of a rotary unit and a power output unit to be linearly movable along their shafts in opposite directions when the cylinders are rotated by power transmission cables operated in conjunction with the drive shaft of a drive motor, thus maintaining desired tension of the transmission cables during an operation of the speed reducing device for achieving a high speed reduction ratio and preventing a backlash of the cables during such operation.
2. Description of the Prior Art
FIG. 1 is a perspective view of a conventional speed reducing device. As shown in the drawing, the conventional speed reducing device comprises a longitudinal drive shaft 120 axially extending from a drive motor 140. A first power transmission cable 180 is fixed to the external surfaces of two first cylinders 220 of a rotary unit 200 at its opposite ends. This first transmission cable 180 is also wound around the drive shaft 120 of a drive motor 140 several times at its middle portion. Therefore, the cable 180 can be wound around or unwound from the two first cylinders 220 while rotating the cylinders 220 in response to a rotation of the drive shaft 120.
A rotating shaft 240 is axially fixed to the center of one end of each first cylinder 220. A second power transmission cable 160 is fixed to the external surfaces of the rotating shafts 240 of the two first cylinders 220 at its opposite ends. This second transmission cable 160 is also wound around the second cylinder 320 of a power output unit 300 several times at it middle portion. The second transmission cable 160 can be thus wound around or unwound from the rotating shafts 240 of the two first cylinders 220 while rotating the second cylinder 320 of the power output unit 300 in accordance with a rotation of the two first cylinders 220. Therefore, the rotating force of the drive motor 140 is transmitted to the power output unit 300 through the drive shaft 120, the first transmission cable 180, the rotary unit 200, and the second transmission cable 160.
In the conventional speed reducing device, the first cable 180 is fixed to one of the two first cylinders 220 at one end thereof, and extends from the first cylinder 220 to be wound around the drive shaft 120 several times prior to being fixed to the other first cylinder 220 at the other end thereof.
When the drive shaft 120 is rotated in a direction by the rotating force of the motor 140, the first cable 180 is unwound from one of the two first cylinders 220, and is wound around the other first cylinder 220, thus finally rotating the power output shaft 340 of the power output unit 300. In such a case, the first transmission cable 180 is moved in either direction in accordance with a rotating direction of the drive shaft 120.
However, the conventional speed reducing device has the following problems. That is, when the first transmission cable 180 is wound around or unwound from the two first cylinders 220 in accordance with a rotation of the drive shaft 120, it is almost impossible to maintain a desired tension of the first cable 180 at portions between the drive motor 120 and the two first cylinders 220 during the rotation of the drive shaft 120. That is, the first transmission cable 180 is undesirably loosened to lose its desired tension when the speed reducing device is operated to achieve a high speed reduction ratio. In such a case, the speed reducing device creates a backlash of the first cable 180.
Due to such a backlash created by the uneven tension of the first transmission cable 180, it is almost impossible to appropriately transmit the rotating force of the first cylinders 220 to the power output unit 300 through the second transmission cable 160. Such a backlash also prevents the speed reducing device from achieving a desired high speed reduction ratio.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a backlash-free speed reducing device, which is designed to allow all the rotatable cylinders of a rotary unit and a power output unit to be linearly movable along their shafts in opposite directions when the cylinders are rotated by power transmission cables operated in conjunction with the drive shaft of a drive motor, thus maintaining desired tension of the transmission cables during an operation of the speed reducing device for achieving a high speed reduction ratio and preventing a backlash of the cables during such operation.
In order to accomplish the above object, the present invention provides a backlash-free speed reducing device, comprising a drive unit consisting of a drive motor, with a drive shaft axially extending from the drive motor; a first power transmission cable wound around the drive shaft a predetermined number of times; a rotary unit having a least one first rotatable cylinder, with the first transmission cable fixed to the external surface of the first rotatable cylinder at an end thereof and wound around or unwound from the first rotatable cylinder in response to a rotation of the drive shaft, the first rotatable cylinder being concentrically fitted over a rotating shaft such that the first rotatable cylinder is linearly movable along the rotating shaft in opposite directions; a second power transmission cable fixed to the external surface of the rotating shaft of the rotary unit at one end thereof and wound around the rotating shaft a predetermined number of times; and a power output unit having a second rotatable cylinder, with the second transmission cable wound around the second rotatable cylinder, the second rotatable cylinder being concentrically fitted over a power output shaft.
In the backlash-free speed reducing device, the rotary unit preferably has two first rotatable cylinders concentrically fitted over two rotating shafts, respectively, such that the two first rotatable cylinders are linearly movable along the two rotating shafts.
The first transmission cable is fixed to the external surfaces of the two first rotatable cylinders at opposite ends thereof, and is wound around or unwound from the first rotatable cylinders in response to a rotation of the drive shaft.
The first rotatable cylinder is linearly movable along the rotating shaft in opposite directions.
In addition, the second rotatable cylinder is linearly movable along the power output shaft in opposite directions.
In the backlash-free speed reducing device, a first fixing hole is formed on the external surface of the first rotatable cylinder so as to fix the end of the first transmission cable on the first rotatable cylinder.
In the backlash-free speed reducing device, a second fixing hole is formed on the external surface of the rotating shaft of the first rotatable cylinder so as to fix the end of the first transmission cable on the rotating shaft.